package org.bouncycastle.util.encoders;

/**
 * a buffering class to allow translation from one format to another to be done in discrete chunks.
 */
public class BufferedDecoder {
    protected byte[] buf;
    protected int bufOff;

    protected Translator translator;

    /**
     * @param translator
     *            the translator to use.
     * @param bufSize
     *            amount of input to buffer for each chunk.
     */
    public BufferedDecoder(Translator translator, int bufSize) {
        this.translator = translator;

        if ((bufSize % translator.getEncodedBlockSize()) != 0) {
            throw new IllegalArgumentException("buffer size not multiple of input block size");
        }

        buf = new byte[bufSize];
        bufOff = 0;
    }

    public int processByte(byte in, byte[] out, int outOff) {
        int resultLen = 0;

        buf[bufOff++] = in;

        if (bufOff == buf.length) {
            resultLen = translator.decode(buf, 0, buf.length, out, outOff);
            bufOff = 0;
        }

        return resultLen;
    }

    public int processBytes(byte[] in, int inOff, int len, byte[] out, int outOff) {
        if (len < 0) {
            throw new IllegalArgumentException("Can't have a negative input length!");
        }

        int resultLen = 0;
        int gapLen = buf.length - bufOff;

        if (len > gapLen) {
            System.arraycopy(in, inOff, buf, bufOff, gapLen);

            resultLen += translator.decode(buf, 0, buf.length, out, outOff);

            bufOff = 0;

            len -= gapLen;
            inOff += gapLen;
            outOff += resultLen;

            int chunkSize = len - (len % buf.length);

            resultLen += translator.decode(in, inOff, chunkSize, out, outOff);

            len -= chunkSize;
            inOff += chunkSize;
        }

        if (len != 0) {
            System.arraycopy(in, inOff, buf, bufOff, len);

            bufOff += len;
        }

        return resultLen;
    }
}
